Demonstrations shutting down the roads around Parliament and Whitehall to call for urgent action on the climate change and wildlife loss have continued into a third day, including mothers with babies marching on Downing Street.
Metropolitan Police Commissioner Cressida Dick said thousands of officers from the London force and colleagues from around the country were working long hours in challenging conditions.
"They have managed so far to secure the bridges and clear the arterial routes through London, and thereby minimise disruption," she said.
The National Police Chiefs' Council said 500 officers are being drafted in from across England and Wales, with police being sent from all the 10 regional organised crime units that cover the two countries. This includes officers from North Yorkshire, South Yorkshire, West Yorkshire and Humberside Police.
A National Police Coordination Centre spokesman said: “The National Police Coordination Centre manages requests for mutual aid, and has received a request from the Metropolitan Police Service. Forces routinely share officers through mutual aid to ensure an appropriate police presence exists where there is increased demand for it.
North Yorkshire Police has issued a statement confirming officers and resources are being sent to London to assist with the policing of the protests.
A force spokesman said: “As part of national mutual aid arrangements, many forces, including North Yorkshire Police, are providing officers and resources to assist with the policing of protests in London.
“When a request for mutual aid is made, we assess what support can be provided, ensuring our local needs are not adversely affected.
“Similarly, the benefit of mutual aid is that if there is an occasion when we require additional support, we can make a mutual aid request in order to ensure we can effectively deal with the matter, while continuing to deliver our high quality, day-to-day policing service to the people of North Yorkshire.”
On Wednesday morning, elderly protesters were arrested outside Downing Street, with people carried and led out of the main road in Whitehall while onlookers sang and shouted "we love you".
Meanwhile, Leeds North West MP Alex Sobel joined the protests, despite warnings he could be arrested if he was to do so.
The Labour MP revealed he is working on a bill with the climate action group to force the Government to meet their three demands for politicians to tell the truth, to commit to carbon neutrality by 2025, and to set up a citizen’s assembly to help tackle the environmental issues faced.
Mr Sobel said: “I’m here right in front of Parliament because the Government hasn’t declared a climate emergency, they haven't conceded to any of three demands of Extinction Rebellion, and action needs to happen immediately.
“I’m working with Extinction Rebellion on a Private Member’s Bill - because the Government aren’t bringing forward a bill - to try and meet some or all of Extinction Rebellion’s three demands and I’m hoping to put that down in the new session.”
The latest protests come after almost 600 Extinction Rebellion protesters were arrested in the first two days of their two-week demonstration in London.
Officers detained 261 people in the UK capital on Tuesday amid activists gluing themselves to buildings and refusing to move when prompted by the Metropolitan Police.
That came after 319 were arrested on Monday on the first day of the international action, which is taking place in cities across the world to demand more be done by governments to tackle climate change.
Disruption is expected for the rest of the week, with protesters set to target City Airport in east London with a peaceful sit-in on Thursday.